A variety of useful articles may be formed using thermally sensitive polymers, such as vinylidene chloride interpolymers. In the past, the practice generally was to extrude the vinylidene chloride interpolymer directly from the powder form in which it is recovered after polymerization. Because of the convenience of shipping and handling, it is desirable to form the vinylidene chloride interpolymer into pellets prior to final extrusion.
With the demand for increased extrusion rate, the processing conditions to which particulates are exposed have become more demanding. When melt processed, conventional particulates of vinylidene chloride interpolymers have a tendency to generate particulate degradation products (i.e., carbonaceous material, gels, or fish eyes) in the extrudate, particularly when the vinylidene chloride interpolymer is exposed to relatively long residence times in the melt processing equipment.
To control the generation of particulate degradation products during melt processing, processing aids such as lubricants (e.g., internal and external types), olefinic waxes and oils, and polyolefins have been blended with the vinylidene chloride interpolymer prior to fabrication into a final product. However, it has been found that, after exposure to desirable processing temperatures, a certain lag time exists before the blended processing aids function effectively. It is during this lag time in the melt processing equipment that the vinylidene chloride interpolymer is particularly susceptible to decomposition.
It is desirable to produce a particulate of a vinylidene chloride interpolymer which is capable of being extruded, in either powder or pellet form, without having an unacceptable level of degradation products in the extrudate. It is to this goal that the present invention is directed.